The work described herein consists of the molecular cloning of the avian apoVLDL II gene. The gene has been cloned in the lambdaphage vector Charon 4a, together with several thousand nucleotides of flanking sequence. It has been demonstrated that this gene is not normally expressed in roosters and that following administration of estrogen there is a qualitative change in the apoprotein composition of very low density lipoprotein, resulting in a polypeptide profile undistinguishable from that of the hen.